1. Field
The presently disclosed subject matter relates to outer casings for vehicle lamps, vehicle lamps using the outer casing and manufacturing methods for the outer casing and the vehicle lamp. More particularly, the disclosed subject matter relates to outer casings utilizing a laser welding method, in which a joint portion between an outer lens and a casing can be welded with confidence by a general laser welder, and to vehicle lamps using the outer casings, which can incorporate various lamps such as a tail lamp with a high airtight structure, and further to methods for manufacturing the outer casings and the vehicle lamps.
2. Description of the Related Art
Conventional general vehicle lamps frequently incorporate various lamps such as a headlight, a position lamp, a tail lamp, a turn signal lamp, a stop lamp and the like into an outer casing, which is devised so as to match with a design of a vehicle as a front and rear combination lamp. The outer casing is generally composed of a casing to incorporate the various lamps and an outer lens attached to the casing so that light emitted from the various lamps can be emitted in a light-emitting direction for each of the lamps.
The outer casing may also perform a sealing function to protect the various lamps from a fluid such as rain, a dust such as dirt on a road, etc. In addition, in accordance with a trend of automotive lighting and for purpose of an improvement of fuel efficiency, the outer casing is typically reduced in weight, along with the various lamps incorporated therein, while maintaining an adequate mechanical strength.
Accordingly, the outer lens, which can be formed in a thin thickness, has been constantly required to cause a reduction in weight for headlights in addition to efficiently transmitting the lights emitted from the various lamps. Moreover, even when the outer lens can be formed in a thin thickness, the outer lens is attached to the casing with confidence while the outer casing is generally air proof and has an adequate mechanical strength.
Hence, a conventional outer casing that can satisfy certain customer needs is disclosed in Patent document No. 1, in which a joint portion between the outer lens and the casing can be fixed with confidence using a jointing material such as a sealing material, an adhesive material, a hot-melt adhesive material, etc. On the other hand, a conventional jointing method is disclosed in Patent document No. 2, in which an outer lens is attached to a casing by a laser welding method without using the jointing material.
FIG. 11 is a schematic side cross-sectional view depicting a conventional laser welding method for attaching an outer lens to a casing used for a vehicle lamp, which is disclosed in Patent document No. 2. The conventional laser welding method includes: preparing the casing 80 having a jointing surface 85; preparing the outer lens 82 having a joint portion 81 made from a plastic having a permeability of laser beam, and the joint portion 81 having an end surface 84; contacting the end surface 84 of the outer lens 82 with the jointing surface 85 of the casing 80; and emitting a laser beam 83 on said contacting surface between the end surface 84 and the jointing surface 85 of the casing 80 from a laser head 86 via the joint portion 81 of the outer lens 82, wherein at least one of the end surface 84 and the jointing surface 85 is formed in a fine concavo-convex shape.
In this case, the laser beam 83 may be emitted on the contact surface including the fine concavo-convex shape via the jointing portion 81, and the end surface 84 of the outer lens 82 may be attached to the jointing surface 85 of the casing 80 in a substantially planar fashion by crushing (or placing pressure upon) the fine concavo-convex shape on the contacting surface between the end surface 84 of the outer lens 82 and the jointing surface 85 of the casing 80.
According to the conventional laser welding method, the laser beam 83 is emitted after the end surface 84 of the outer lens 82 contacts with the jointing surface 85 of the casing 80 with accuracy so that a misalignment does not occur with respect to each other. The laser beam 83 may be emitted by a gauss distribution, in which a middle portion of the laser beam 83 emits a high light energy, and a peripheral portion of the laser beam 83 emits a low light energy as compared with the middle portion of the laser beam 83.
Accordingly, because a laser beam having a high light energy may emit at a middle portion on the contact portion between the end surface 84 of the outer lens 82 and the jointing surface 85 of the casing 80, and a laser beam having a relatively low light energy may emit at a peripheral portion on the contact portion between the end surface 84 of the outer lens 82 and the jointing surface 85 of the casing 80, the outer lens 82 may be attached to the casing 80 with confidence in a state of mutual melting at the middle portion on the contact portion.
However, it may be difficult for the laser welding method to attach the outer lens 82 to the casing 80 with absolute accuracy in a mutual state of a thermal melting at the peripheral portion on the contact portion, because the peripheral portion of the contact portion may be subject to a state of non-thermal melting. In addition, it may difficult using the conventional laser welding method to align the outer lens 82 with the casing 80 on all circumferences with accuracy.
While drivers sit at the wheel, vehicle lamps may be subject to vibrations caused by traffic, shocks, etc. Additionally, the insides of the vehicle lamps may attain a high temperature during operation especially in summer. The outsides of the vehicle lamps may attain a low temperature regardless of operation in winter, although the insides may still attain a high temperature during operation. Therefore, when the vehicle lamps have been used for a long time, in the vehicle lamps manufactured by the conventional laser welding method, dirt and dust, rain water and the like may penetrate from a small void in the contact portion between the end surface 84 of the outer lens 82 and the jointing surface 85 of the casing 80.
Especially, when a misalignment occurs between the end surface 84 of the outer lens 82 and the jointing surface 85 of the casing 80, the small void in the contact portion may allow easy penetration of dirt and dust, rain water, etc. As a result, the dirt and dust, the rain water and the like may degrade the performance of the vehicle lamps, and also may cause failures of the vehicle lamps in the worst case.
The above-referenced Patent Documents and an additional Patent Document are listed below and are hereby incorporated with their English abstracts and specification in their entireties.    1. Patent Document No. 1: U.S. patent application Ser. No. 13/433,104    2. Patent Document No. 2: Japanese Patent Application Laid Open JP2005-339,989    3. Patent Document No. 3: U.S. Pat. No. 7,665,868    4. Patent Document No. 4: U.S. Pat. No. 8,100,569    5. Patent Document No. 5: U.S. patent application Ser. No. 13/358,500
The disclosed subject matter has been devised to consider the above and other problems, features, and characteristics. Thus, embodiments of the disclosed subject matter can include outer casings for vehicle lamps, in which an outer lens can be attached to a casing including a peripheral portion of a joint portion thereof with confidence by a general laser welder. The disclosed subject matter can also include vehicle lamps using the outer casings, which can incorporate various lamps such as a headlight, a tail lamp, a position lamp, a turn signal lamp, a stop lamp and the like with a high airtight structure and an adequate mechanical strength while preventing a misalignment between the outer lens and the casing.